The present invention relates to a lower vehicle-body structure of an automotive vehicle which comprises a seat-attaching bracket supporting a seat where a passenger is seated.
In general, the seat where the passenger is seated is fixed to a portion of a vehicle body which has relatively-high rigidity in a cabin of the automotive vehicle in order to secure the ride comfort (ride quality) of the passenger. For example, in a structure disclosed in Japanese Patent Laid-Open Publication No. 2010-228482, a front portion of the seat where the passenger is seated is supported at a cross member 20 (No. 2 cross member) which interconnects right-and-left side sills 6 via a tunnel portion 2 of a floor panel 1 which forms a bottom face of the cabin.
Meanwhile, a rear portion of the seat is supported at a seat-attaching bracket (connecting member 35) which is joined both to a cross member 30 (No. 2.5 cross member) interconnecting the right-and-left side sills 6 via the tunnel portion 2 at a position located in back of the cross member 20 and another seat-attaching bracket (connecting member 36) which is joined both to the cross member 30 and the tunnel portion 2.
In other words, in the structure disclosed in the above-described patent document, when another vehicle collides with a side portion of an own vehicle or the side portion of the own vehicle collides with an obstacle, the seat where the passenger is seated is fixed onto a load transmission path where a side-collision load as a collision load applied from a vehicle side is transmitted/dispersed from one side to the other side in a vehicle width direction.
Herein, the structure disclosed in the above-described patent document is configured such that the seat is fixedly fastened to an inward-side end portion, in the vehicle width direction, of a roughly flat-plate shaped upper wall portion of the seat-attaching bracket (connecting member 35) which is joined to the cross member 30 and the side sill 6.
Accordingly, the upper face portion of the seat-attaching bracket (connecting member 35) has a large area, so that its surface rigidity against a load which is applied in a vehicle vertical direction tends to be low. Further, since a weight of the passenger tends to act on the rear portion of the seat in a state where the passenger is seated, there is a problem that if the surface rigidity of the upper face portion is low, the upper face portion may be easily deformed due to vertically-directional vibration of a vehicle body which is generated during vehicle traveling in a case where the seat-attaching bracket (connecting member 35) supports the rear portion of the seat as disclosed in the above-described patent document.
In this case where the upper face portion is easily deformed due to the vertically-directional vibration of the vehicle body, when the automotive vehicle rides over a slope, for example, the upper face portion of the seat-attaching bracket (connecting member 35) starts its deformation in an early stage, so that there is a concern that an urethane cushion forming the seat may not sufficiently damp the vertically-directional vibration of the vehicle body, so that the vibration may be transmitted to the passenger improperly.
Additionally, if the seat rear portion is made to swing in the vehicle vertical direction by the deformation of the upper face portion, a seatback of the seat swings in a vehicle longitudinal direction in accordance with this vertically-directional swing. Thereby, a head portion of the passenger is forced to swing, so that there is a concern that the ride comfort of the passenger may be deteriorated.